Regeneration of a Capacitive Deionization System

ABSTRACT

Embodiments of the invention provide a method of regenerating a capacity of a flow-through capacitor. A target value for a water property concentration in a discharge water stream exiting the flow-through capacitor is established. A feed value for the water property concentration in a feed water stream entering the flow-through capacitor is measured. An amount of the water property concentration to be added to the feed water stream is calculated based on the feed value to achieve the target value for the water property concentration in the discharge water stream. An amperage of the flow-through capacitor and a flow rate through the flow-through capacitor is controlled to add ions to the feed water stream to achieve the target value for the water property concentration in the discharge water stream. In some embodiments, the amperage can be set and the flow rate controlled to achieve the target concentration.

BACKGROUND

This application is directed at systems, devices, and methods for thetreatment of water using electrochemical treatment.

Capacitive deionization can be used to remove electrically-chargedconstituents, such as ions, from water. In capacitive deionizationsystems, a stream of water passes through one or more flow-throughcapacitors which include pairs of polarized electrodes. To treat thestream as the water passes between the electrodes, a voltage potentialis established between the electrodes. This voltage potential causesconstituents in the water to be attracted to and at least temporarilyretained on one of the electrodes while the comparatively purified wateris allowed to exit the capacitor.

After some time of treatment, the electrodes will become saturated withconstituents such that the electrodes can no longer effectively removeconstituents from the stream of water. To regenerate the capacity of theflow-through capacitor, the flow-through capacitor may be set todischarge the captured constituents. Typically, this discharge occurs byremoving the voltage potential or by temporarily applying a voltagepotential in an opposite direction to the voltage potential establishedduring treatment, thereby releasing the constituents from theelectrodes. During discharge, the effluent water carrying theconstituents is typically routed to a waste line.

SUMMARY

Some embodiments of the invention provide a method of regenerating acapacity of a flow-through capacitor having at least a pair ofelectrodes spaced from one another to accommodate a flow of water andconfigured to transfer ions between the pair of electrodes and thewater. A target value for a water property concentration in a dischargewater stream exiting the flow-through capacitor is established. A feedvalue for the water property concentration in a feed water streamentering the flow-through capacitor is measured. An amount of the waterproperty concentration to be added to the feed water stream iscalculated based on the feed value to achieve the target value for thewater property concentration in the discharge water stream. An amperageof the flow-through capacitor and a flow rate through the flow-throughcapacitor is controlled to add ions to the feed water stream to achievethe target value for the water property concentration in the dischargewater stream.

Some embodiments of the invention provide a method of regenerating acapacity of a flow-through capacitor having at least a pair ofelectrodes spaced from one another to accommodate a flow of water andconfigured to transfer ions between the pair of electrodes and thewater. An amperage set point for the flow-through capacitor and a targetconcentration for a water property concentration in a discharge waterstream exiting the flow-through capacitor is established. A feed valuefor the water property concentration in a feed water stream entering theflow-through capacitor is measured. An ion transfer to the feed waterstream is calculated based on the amperage set point and a flow raterequired to achieve the target concentration for the water propertyconcentration in the discharge water stream. The flow rate through theflow-through capacitor is controlled to achieve the target concentrationfor the water property concentration in the discharge water stream whilemaintaining the amperage set point of the flow-through capacitor.

Some embodiments of the invention provide a controller for performingone or both of methods described above.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a capacitive deionization system having aflow-through capacitor and a hydropneumatic storage tank according toone embodiment of the invention.

FIG. 2 is a schematic of a capacitive deionization system having aflow-through capacitor and an atmospheric tank according to anotherembodiment of the invention.

FIG. 3 is a schematic of a flow-through capacitor.

FIG. 4 is a partial cross-sectional side view of a vessel containing aflow-through capacitor in which the vessel has a valve attached theretothat is configured to selectively route water through the flow-throughcapacitor and the valve performs the various functions provided by someof the multiple separate valves from FIGS. 1 and 2.

FIG. 5 is a process flowchart illustrating the general operation of acapacitive deionization system with a flow-through capacitor accordingto one form of the inventive method.

FIG. 6 is a graph of indicating the current and voltage values of theflow-through capacitor over one example of an operational cycle.

FIG. 7 is a process flowchart illustrating a treatment cycle accordingto one aspect of the inventive method.

FIG. 8 is a process flowchart illustrating a regenerative cycleaccording to one aspect of the inventive method.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having” and variations thereof herein ismeant to encompass the items listed thereafter and equivalents thereofas well as additional items. Unless specified or limited otherwise, theterms “mounted,” “connected,” “supported,” and “coupled” and variationsthereof are used broadly and encompass both direct and indirectmountings, connections, supports, and couplings. Further, “connected”and “coupled” are not restricted to physical or mechanical connectionsor couplings.

The following discussion is presented to enable a person skilled in theart to make and use embodiments of the invention. Various modificationsto the illustrated embodiments will be readily apparent to those skilledin the art, and the generic principles herein can be applied to otherembodiments and applications without departing from embodiments of theinvention. Thus, embodiments of the invention are not intended to belimited to embodiments shown, but are to be accorded the widest scopeconsistent with the principles and features disclosed herein. Thefollowing detailed description is to be read with reference to thefigures, in which like elements in different figures have like referencenumerals. The figures, which are not necessarily to scale, depictselected embodiments and are not intended to limit the scope ofembodiments of the invention. Skilled artisans will recognize theexamples provided herein have many useful alternatives and fall withinthe scope of embodiments of the invention.

FIGS. 1 and 2 illustrate capacitive deionization systems 10, 110 withoutand with an atmospheric tank 163, respectfully. These capacitivedeionization systems 10, 110 are designed to receive feed water andtreat this water using capacitive deionization along with other optionaltreatment processes to remove constituents from the water. Systems ofthis type can be used, for example, to treat water to improve waterquality for a particular use or to re-claim valuable constituents (e.g.,metals) from the water stream. Accordingly, while a system for watertreatment is described, the systems and methods described herein can beapplied to any application in which a flow-through capacitor may beused.

Additionally, while FIGS. 1 and 2 illustrate the use of multiple valvesto route water through the systems 10, 110, other valve arrangements canbe used, such as, for example, a single valve arrangement attached tothe flow-through capacitor as shown in FIG. 4 in which the single valveperforms the function of many of the valves shown in FIGS. 1 and 2.

Returning now to the description of FIGS. 1 and 2, on the inlet side ofeach capacitive deionization system 10, 110, a feed water inlet 12, 112selectively provides water for filtration and deionization to aflow-through capacitor 26, 126. In the embodiment shown, the stream ofwater flows from the feed water inlet 12, 112 to the flow-throughcapacitor 26, 126 by passing through an inlet line having sequentiallydisposed thereon an iron filter 14, 114, a carbon and/or sedimentpre-filter 20, 120, and an inlet isolation valve 16, 116 (when open).For the capacitive deionization system 10 of FIG. 1 there is also a pump17 disposed between the iron filter 14 and the pre-filter 20 which canbe used to maintain the pressure in the system 10. The pump 17 orpressure source can be differently placed or connected to the system 10in other arrangements and so the illustrated embodiment is only onepossible configuration of the system 10. The inlet line also includes anumber of indicators and sensors including a pressure sensor 18, 118, aconductivity indicator 22, 122 and a flow transducer 25, 125 disposedbetween the inlet isolation valve 16, 116 and the flow-through capacitor26, 126.

Many of the elements between the feed water inlet 12, 112 and theflow-through capacitor 26, 126 are optional. For example, the ironfilter 14, 114 and/or the pre-filter 20, 120 may be absent and the feedwater inlet 12, 112 can be directly coupled to or directly incommunication with the inlet isolation valve 16, 116. Likewise, the ironfilter 14, 114 and/or the pre-filter 20, 120 can be replaced with orsupplemented by another pre-treatment process, if desired.

As will be described in more detail below with reference to FIG. 3, theflow-through capacitor 26, 126 is capable both of deionizing water bythe removal of charged constituents from the water and of periodicallydischarging the collected constituents to regenerate the capacity of theflow-through capacitor 26, 126.

On the outlet side of the flow-through capacitor 26, 126, the stream ofwater exits the flow-through capacitor 26, 126 from an outlet line 52,152 and passes through a number of components to ultimately arrive ateither a treated water outlet 76, 176 or a drain 58, 158. The treatedwater outlet 76, 176 can provide treated water to, for example, aresidential plumbing system, whereas the drain 58, 158 accommodates thedisposal of impurity-rich or constituent-rich water during iondischarge, cleaning, or regeneration of the flow-through capacitor 26,126. In some embodiments in which the system is being used to re-claimconstituents (such as metals) from a water stream, the water from thedrain 58, 158 may not be disposed but may instead be collected forfurther processing.

In both capacitive deionization systems 10, 110, the outlet line 52, 152of the flow-through capacitor 26, 126 branches in one direction to thedrain 58, 158 and in the other direction to the treated water outlet 76,176. In the embodiments shown in FIGS. 1 and 2, the path of flow of thewater from the outlet line 52, 152 is determined by the configuration ofcontrol valves after the branch. On the way to the drain 58, 158 andafter the branch in the outlet line 52, 152, there is a drain controlvalve 56, 156 which, if open, places the outlet line 52, 152 in fluidcommunication with the drain 58, 158. On the pathway from the outlet 52,152 to the treated water outlet 76, 176 and after the branch, there is atreated water control valve 62, 162 which, if open, permits water toflow toward the treated water outlet 76, 176. In the embodiments ofFIGS. 1 and 2, only one of these two valves will be open, while theother will be closed.

Two lines provide routes for some or all water to be diverted around theflow-through capacitor 26, 126. The first of these lines is a blend line88, 188 which can be used to selectively blend treated water that haspassed through the flow-through capacitor 26, 126 with untreated waterthat has been diverted around the flow-through capacitor 26, 126 fordelivery to the treated water outlet 76, 176. The blend line 88, 188branches from a portion of the inlet line before the flow transducer 25,125 and the flow-through capacitor 26, 126 and re-connects with thetreated water outlet line after the flow-through capacitor 26, 126 andthe treated water control valve 62, 162. Along the blend line 88, 188,there is a blend valve 90, 190 which can be used to select a flow ofwater that is permitted to pass through the blend line 88, 188.

The second circumvention line is a manual bypass line 84, 184 which canbe used to entirely bypass the flow-through capacitor 26, 126 and blendline 88, 188 when the inlet isolation valve 16, 116 is closed. In theembodiment shown in FIGS. 1 and 2, the bypass line 84, 184 branches fromthe inlet line after the carbon and sediment pre-filter 20, 122 andprovides the water downstream of the flow-through capacitor 26, 126.Along the bypass line 84, 184, there can be a manual bypass valve 86,186 which is closed when the manual bypass line 84, 184 is not in use.If the system 10, 110 is to be circumvented or bypassed in order to, forexample, perform maintenance or re-route water during a power failure,then the inlet isolation valve 16, 116 is closed (in some embodiments, awater outlet isolation valve, such as the valve 74 in FIG. 1, may alsobe closed) and the manual bypass valve 86, 186 is open to route wateraround the flow-through capacitor portion of the system.

Returning now to the description of the outlet side of the capacitivedeionization systems 10, 110, it can be seen that the arrangements ofthe capacitive deionization systems 10, 110 differ downstream of thetreated water control valve 62, 162. Most notably, FIG. 1 depicts acapacitive deionization system 10 having only a hydropneumatic storagetank 72, while FIG. 2 depicts a capacitive deionization system 110 thatalso has an atmospheric storage tank 163.

Looking first at the embodiment lacking the atmospheric tank in FIG. 1,there can be an optional pump (not shown) which pumps either the waterthat has passed through treated water control valve 62 (meaning thatsome portion of the water has been treated by the flow-through capacitor26) and/or through the blend line 88. The upstream pump 17 can alsoprovide a source of system pressure. This water is transporteddownstream through a line to the hydropneumatic storage tank 72 thatreceives and stores pressurized water. Pressure sensors can be connectedto the hydropneumatic storage tank 72 to monitor the air or waterpressure within the air chamber in the hydropneumatic tank 72. Ondemand, this hydropneumatic storage tank 72 delivers water underpressure to the treated water outlet 76. Additionally, a pressure sensor66 and a conductivity indicator 68 are attached to the line between thetreated water control valve 62 and an outlet isolation valve 74 that islocated upstream of the hydropneumatic storage tank 72 and the treatedwater outlet 76.

In the configuration of FIG. 2, the capacitive deionization system 110includes the atmospheric tank 163. Water passing through either thetreated water control valve 162, the blend line 188, and/or the manualbypass line 184 is fed into that atmospheric storage tank 163 where thewater can be temporarily stored. A conductivity indicator 168 can becoupled to the line feeding the atmospheric storage tank 163 from thetreated water control valve 162 and the blend line 188. The atmosphericstorage tank 163 can include one or more level sensors or switches 165,167 that establish whether a minimum water level in the tank 163 hasbeen achieved and/or whether a target maximum water level in the tank163 has been reached. These level switches 165, 167 can also be used todetermine whether the flow rate through the flow-through capacitor 126is nominal or high. One benefit of an atmospheric storage tank 163 isthat the tank 163 can be able to store relatively large volumes oftreated water so that larger quantities of treated water can be suppliedon demand to a connected point of use or plumbing system, even when thesystem is unable to treat a sufficient quantity and or provide aparticular quality of water in real-time.

Water from the storage tank 163 can then be supplied to a pump 164 thatpumps the water downstream through a check valve to an optionalhydropneumatic storage tank 172. If there is a hydropneumatic storagetank 172, then a pressure sensor 170 can be connected to thehydropneumatic tank 172 and can sense the air or water pressure in theair chamber of the hydropneumatic tank 172. The pressure sensor 170 canprovide a signal to the pump 164 indicating if more water needs to bepumped in order to maintain pressure in the tank 172. In the particularembodiment shown, there is also an optional ultraviolet (UV) treatmentsystem 175 positioned downstream of the pump 164 and the hydropneumaticstorage tank 172, but before an isolation valve 174 prior to the treatedwater outlet 176.

Although a hydropneumatic storage tank 172 is shown in FIG. 2, asubstantially constant pressure can be maintained by instead using, forexample, a variable speed pump or another variable pressure source.

FIG. 3 schematically illustrates a flow-through capacitor 26 for thecapacitive deionization of water. The flow-through capacitor 26 can besimilar to the flow-through capacitor 126, and the illustration of FIG.3 is only intended to provide a general understanding of the arrangementof the flow-through capacitor. The actual flow though capacitor caninclude various seals, connectors, sensors, and so forth which areomitted from the schematic for simplicity of description.

The flow-through capacitor 26 includes a stack 27 of individual fluidprocessing cells 28 which are contained in a housing 29 having a waterinlet 30 and a water outlet 31. The flow-through capacitor 26 isconfigured so that, in order for water to pass from the water inlet 30to the water outlet 31 of the flow-through capacitor 26, the water mustpass through the stack 27 of individual processing cells 28. In thestack 27, the water can be deionized during treatment or receiveconstituents during discharge or regeneration. Each cell 28 in the stack27 includes one or more of a combination of the following elements:electrode pairs 32, cation membranes 35, anion membranes 36, and flowspacers 37 which are typically made of a plastic mesh. While the cationand anion membranes can be used to provide improved attachment andstorage of the constituents on the electrodes, the membranes are notrequired and the cells can be manufactured without them. Additionally,the electrode can be constructed to have a two-part electrodeconstruction including a carbon adsorptive electrode layer and a currentcollector.

In the embodiment shown in FIG. 3, each of these cell elements is in theform of a relatively thin layer that is disposed in parallel with theother layers which are stacked upon one another in a repeating patternof first electrode/cation membrane/spacer/anion membrane/secondelectrode/anion membrane/spacer/cation membrane. After the last cationmembrane, there may be another first electrode and the pattern may berepeated. Since any flux of charged constituents occurs as the result ofa voltage difference created between the first and the secondelectrodes, electrode layers can form the bottommost and topmost layersof the stack 27.

To better appreciate the description of the flow-through capacitor 26that follows, it should be understood that FIG. 3 is a cross-sectionalside view taken through the center of one example embodiment of theflow-through capacitor 26. The various cell elements are generally thinplanar layers having central openings that align to form a central flowcolumn 38. Accordingly, for any given layer, the cell elements on theleft and right side of the central flow column 38 are part of the samelayer. Moreover, water is able to flow between the inside of the vesselor housing 29 and the outer periphery of the cell elements of the stack27. This means that the area between the housing 29 and the stack 27 onthe left side and the right side of the schematic are in fluidcommunication with one another.

In FIG. 3, arrows generally depict the pattern of forward flow throughthe flow-through capacitor 26. Although a forward flow direction isshown, in some instances or operational cycles, water can be run throughthe flow through capacitor 26 in a reverse direction. In someembodiments, to achieve a desired flow pattern within the flow-throughcapacitor 26, there can be multiple water inlets or structures thatpromote an even or otherwise desirable water flow pattern through theflow spacers 37 in the stack 27. There can be additional structuralelements that are used to position, electrically connect and/or compresssome or all of the cell elements in the stack 27.

As also shown in FIG. 3, the flow-through capacitor 26 includes manyelectrode pairs 32. In one embodiment, each electrode pair 32 includes afirst electrode 33 (which during treatment acts as a cathode) and asecond electrode 34 (which during treatment acts as an anode). Theelectrodes 33 and 34 can be constructed from high-surface areaelectrically conducting materials such as, for example, activatedcarbon, carbon black, carbon aerogels, carbon nanofibers, carbonnanotubes, graphite, graphene, or mixtures thereof. In some embodiments,the electrodes 33 and 34 can be placed as a separate layer on top of acurrent collector or can alternatively be coated directly onto thecurrent collector.

The first electrodes 33 and the second electrodes 34 are configured andelectrically connected relative to each other to establish a voltagedifference or potential there between. The first electrodes 33 in theflow-through capacitor 26 can be connected to one another and are thenconnected to a power supply. Similarly, the second electrodes 34 in theflow-through capacitor 26 can be connected to one another and are thenconnected to the power supply. Although not depicted in the schematic ofFIG. 3, the electrodes can be connected to one another at their outeredges using peripheral tabs that contact one another or using otherforms of connection. The stack 27 will be arranged so that nearestneighbor electrodes will be of different kinds (i.e., the firstelectrodes will be disposed between the second electrodes andvise-versa). In some embodiments, the various electrodes sets can beinterleaved with one another and arranged so as to place multipleelectrode pairs in series with one another.

Regardless of the specific electrical arrangement and connectivity ofthe electrodes, during operation these first and second electrodes 33and 34 can be differently charged from one another to establish avoltage potential across the electrodes pairs. This voltage potentialcan be used to either draw charged constituents out of the water towardthe electrodes (such as during treatment) or release the collectedconstituents back into the water (such as during regeneration, dischargeor cleaning).

Cation membranes 35 and anion membranes 36 are positioned adjacent tothe first electrode 33 and the second electrode 34, respectively. Thecation membrane 35 and the anion membrane 36 act as charge barriers thatcan be placed between the electrodes 33 and 34 and thecentrally-disposed flow spacer 37. The term “charge barrier” as usedherein and in the appended claims refers to a layer of material that canhold an electric charge and that is permeable or semi-permeable forions. Ions with the same charge signs as that in the charge barriercannot pass through the charge barrier to the corresponding electrode.As a result, ions which are present in the electrode compartmentadjacent to the charge barrier and which have the same charge sign asthe charge in the charge barrier are at least temporarily retained ortrapped in the electrode compartment. A charge barrier can allow anincrease in ion removal efficiency as well as a reduction in the overallenergy consumption for ion removal.

Finally, the plastic mesh flow spacer 37 is disposed between the cationmembrane 35 and the anion membrane 36 (and the corresponding electrodepair 32). This mesh spacer 37 has a pattern similar to a window screenand also has some sections that are thicker than others sections in theheight dimension (the height dimension is generally perpendicular to thedirection of flow through the spacers 37) so that, when the spacer layeris lightly compressed between two other layers such as the cationmembrane 35 and the anion membrane 36, water is able or permitted toflow across the spacer 37 layer and between the corresponding pairs ofelectrodes 33 and 34.

FIG. 3 is only a simplified schematic of the flow-through capacitor 26and does not illustrate all of the mechanical components that can bepart of the flow-through capacitor 26. For example, a flow-throughcapacitor will likely include tens or hundreds of electrode pairs toprovide an appropriate amount of surface area for deionization of ausable amount of treated water. Moreover, while only a single stack isillustrated, multiple modules or trays of cell components can beconstructed. In some embodiments (such as the module shown in FIG. 4),trays containing a number of electrode pairs can be stacked on oneanother and the trays separately or aggregately compressed.

Additionally, although not shown in the schematic of FIG. 3, the variouslayers of the stack are compressed to control the amount of spacebetween the cell components, thereby establishing a cross-section areathrough which the water that can flow through the stack 27. Thiscompression can be done in a number of ways. In one embodiment, apressure plate at the top of the flow-through capacitor can compress thecell components or layers in a direction perpendicular to the directionof fluid flow through the stack 27. A pressure plate such of this typecan be able to apply a variable compressive force by mechanicalfastening (e.g., employing a threaded screw element which can betightened or loosened to adjust compressive force). In otherembodiments, the stack can be divided into multiple portions, such as inmodules, with each portion being separately compressible.

In general operation, water flows enters the flow-through capacitor 26via the water inlet 30 located on a bottom side wall of the housing 29.At this point, the water is able to flow through some volume between ofthe housing 29 and the stack 27. Some applied pressure differential(likely established by the continued inflow of water to the flow-throughcapacitor 26) will then cause water to be forced through the spacers 37of the stack 27 and into the central column 38 at which point it flowsupward and out of water outlet 31. By establishing a voltage differencebetween the electrode pairs 32, charged constituents such as ions can betransferred between the water flowing through the spacers 37 and thecation and anion membranes 35 and 36. The specifics of the control andoperation of the cell will be described in further detail below.

FIG. 4 illustrates one embodiment of a portion of a capacitivedeionization system 410 including a valve 402 positioned on top of avessel 404 that houses a flow-through capacitor 426. In this embodiment,the valve 402 is coupled to the vessel 404 at a single location so thatwater can flow from the valve 402 into the vessel 404 and from thevessel 404 back into the valve 402 through separate channels. A flowpathway can established through the vessel 404 in which the entry andexit channels are provided at the same opening of the vessel.

In FIG. 4, arrows are used to indicate a forward flow of water throughthis section of the system 410. The arrows indicate flow from the valve402 into a chamber 480 of the vessel 404, between the vessel walls andthe flow-through capacitor 426, through the flow-through capacitor 426,up a central column 438 of the flow-through capacitor 426, up a centralcolumn 482 of a compression element 484 that compresses the stack of theflow-through capacitor 426, and returns the flow to the valve 402 to berouted to either a treated water outlet or drain. This forward flow isfor the purposes of illustration only, and the specific direction offlow and the structure used to direct the flow can be different thanthat illustrated.

The valve 402 is a control valve assembly that performs multiplewater-routing functions and can eliminate the need for multiple separatevalves as shown in FIGS. 1 and 2. For example, the valve 402 can havemultiple positions including the following: (1) a service position inwhich all water from an inlet line to the valve is routed into thevessel 404, through the flow-through capacitor 426, and then is directedto a treated water outlet (such as, for example, outlets 76, 176); (2) ablend position in which a portion of water from an inlet line into thevalve 402 is directed into the vessel 404 and through the flow-throughcapacitor 425 while the remainder of the water from the inlet line isnot routed through the flow-through capacitor 426 but is re-combinedwith the water that passes through the flow-through capacitor 426 toblend treated and untreated water; (3) a drain position in which wateris routed through the flow-through capacitor 426 and then routed to adrain line to a drain (such as, for example, drains 58, 158); and (4) aclosed position in which the outlet of the valve 402 is shut so thatwater does not continue to substantially flow through the valve 402 orthe flow-through capacitor 426.

FIGS. 1 and 2 further illustrate that a processor or a controller 78,178 is in electrical communication with the flow-through capacitor 26,126 and many of the components of the capacitive deionization system 10,110. The controller 78, 178 is connected to many of the sensorsincluding the pressure sensor 18, 118, the conductivity indicator 22,122, the flow transducer 25, 125, the pressure sensor 66, theconductivity sensor 68, 168, and level sensors or switches 165, 167. Thecontroller 78, 178 is also connected to a number of valves including thedrain control valve 56, 156, the treated water control valve 62, 162,and the blend valve 90, 190. The controller 78, 178 can also beconnected to a power supply for the flow-through capacitor 26, 126. Onehaving ordinary skill in the art will readily appreciate the fact thatcontroller 78, 178 can potentially include one or more processors,microprocessors, programmable logic controllers, or other suitablesoftware and hardware configurations. Additionally, in alternativeembodiments, the controller can be connected to other system elements ornot connected to some of the system elements depicted. Moreover, thecontroller 78, 178 can provide or be connected to a user interface forpurposes of monitoring a water property (or water propertyconcentration), monitoring system functions, adjusting set points usedfor system control, reviewing operating history, and providingdiagnostics.

For example, with reference to FIG. 1, the controller 78 can providecontrol over the delivery of water to the hydropneumatic tank 72, whenone is present. When one or more pressure sensors sense that the air orwater pressure in the hydropneumatic tank 72 is below a lower set point,the controller 78 opens the control valve 62, turns on forward operationof the pump 17, and turns on the power supply for the flow-throughcapacitor 26 (provided that flow-through capacitor 26 does not requireregeneration, as is described in further detail below) until the air orwater pressure in hydropneumatic tank 72 reaches an upper set point forthe pressure. If the flow-through capacitor 26 requires regeneration,then the controller 78 will close the control valve 62, and removeand/or reverse the charge provided to the flow-through capacitor 26 bythe power supply. The controller 78 opens the drain control valve 56when the ions removed during the regeneration mode are to be dischargedvia the drain 58.

The controller 178 can also provide control over the delivery of waterto the atmospheric tank 163 for a system 110 such as shown in FIG. 2.The controller 178 can be connected to the low level sensor 165 and thehigh level sensor 167 on the atmospheric tank 163. When the high levelsensor 167 senses that the water level in the atmospheric tank 163 isbelow its set point, the controller 178 opens the control valve 162 andturns on the power supply for the flow-through capacitor 126 (providedthat the flow-through capacitor 126 does not require regeneration) untilthe water level in the atmospheric tank 163 reaches the upper set pointof the high level sensor 167. If the flow-through capacitor 126 requiresregeneration, the controller 178 can temporarily close the control valve162, remove and/or reverse the charge provided to the flow-throughcapacitor 126 by the power supply, and open the control valve 156 so theions removed during the regeneration cycle are discharged via the drain158. If the water level in the atmospheric tank 163 falls below thelower set point of the low level sensor 165 and the flow-throughcapacitor 126 is unable to keep up with demand, then the controller 178opens the blend valve 190 until the water level in the atmospheric tank163 reaches the upper set point of the low level sensor 165, temporarilycircumventing the flow-through capacitor 126 for particularly high waterdemand. In this instance, the conductivity sensor 168 can monitor thewater entering the atmospheric tank to ensure that the water qualitydoes not exceed a unacceptable level.

The level sensors 165, 167 can be used to measure and adjust a flow ofwater through the flow-through capacitor 26, 126. In some embodimentsthere can be one or more level sensors or switches that can be used toperform such operations or measurements.

Additionally, the controller 78, 178 can use measured qualities (e.g.,pressures and conductivities) and related logic to perform variousoperations and provide instructions for, for example, opening and/orclosing valves, routing the water stream either in full or in partthrough various lines of the system, and operating or adjustingoperational parameters of the flow-through capacitor.

The underlying structure of some embodiments of the capacitivedeionization systems 10, 110, 410 having now been explained, the generaloperation of the systems 10, 110, 410 and the various operational cyclesof the systems 10, 110, 410 will be described in further detail.

General Operation

During typical operation, the capacitive deionization system 10, 110 andthe flow-through capacitor 26, 126 cycles between four principaloperating modes: a standby mode in which substantially no flow of wateris processed by the flow-through capacitor 26, 126, a treatment mode inwhich the flow-through capacitor 26, 126 removes charged constituentsfrom the stream of water passing there through, a regeneration mode inwhich the flow-through capacitor 26, 126 eliminates or discharges thecollected charged constituents to regain capacity for further treatment,and a cleaning mode in which the flow-through capacitor 26, 126 ismaintained to prevent scaling and other potential effects of long termcycling. The system 10, 110 can be configured to toggle between thestandby, treatment, regeneration, and cleaning modes based on a numberof criterion including, but not limited to, the demand for water (eitherin an attached hydropneumatic or atmospheric tank or in the greaterplumbing system), detected feed water and treated water properties(e.g., water pressures, water conductivities, and so forth), andmeasured values of system parameters (e.g., properties relating to theoperation of the flow-through capacitor).

To simplify understanding of the operation of the system for thepurposes of this application, these four principal operating modes willbe the most thoroughly described. The system is not limited to merelythe described operational modes nor does the system necessarily need toinclude all four of the modes described in detail herein. The system caninclude other modes of operation such as, for example, diagnostic modes.Likewise, the system can include functionality that includes faultdetection and/or permits the operation of the system during a powerfailure. Operation of the system can be either manually controlled(e.g., at the direct instruction of a user) or automatically controlled(e.g., according to pre-established programs). When the system isautomatically controlled, it will be at the direction of the controller78, 178 which has the ability to sense conditions in the system 10, 110and to instruct or control the operation of various components of thesystem 10, 110.

The specific operation of the system will be described in furtherdetail. It should be appreciated that any language describing operationof the system or flow-through capacitor, regardless of whether or notthe controller is specifically mentioned, should be read as beingpossible to do with or through the controller. For example, if thesystem is described as monitoring a current value, this monitoringfunction can be performed by the controller. Likewise, when the systemor flow-through capacitor operation is changed, instructions can beprovided by the controller.

Current-Regulated Operation

The basic principle of operation in capacitive deionization systems hasbeen that charged constituents can be transferred between the water andthe electrodes (and/or membranes) of a flow-through capacitor bycontrolled and selective application of a voltage differential betweenthe electrodes. Since the voltage difference or voltage potential is the“driver” of ion transfer, prior systems have focused on controlling orregulating a voltage potential to operate the capacitive deionizationsystem.

Methods of controlling operation of a capacitive deionization system andcontrollers for a capacitive deionization system are disclosed. Amongother things, the disclosed methods and controllers utilize a differentmode of operating a flow-through capacitor than that which is found inconventional systems. Whereas conventional systems aim to regulate thevoltage potential established across the electrodes, the methods andcontrollers described herein rely on the control and monitoring ofcurrent. By integrating the current or other value over the time ofoperation, a capacitive deionization system can be operated in such amanner as to more accurately reflect the actual state of the capacitor.

The methods, systems, and controllers described herein apply a new anduniquely different methodology to the operation of a capacitivedeionization system. Instead of controlling and maintaining a specificvoltage potential or differential between the electrodes during thetransfer of ions or charged constituents, the methods, systems, andcontrollers of some embodiments of the invention monitor and regulatethe current of the flow-through capacitor during the operation of thesystem. Since the flux of charged particles directly relates to thecurrent and amount of treatment or discharge occurring,current-regulated control is a useful proxy by which to run and measurecapacitive deionization system operation. Although a voltage is appliedto create the potential across the electrodes in the flow-throughcapacitor, the applied voltage is selected to obtain a particularcurrent in the flow-through capacitor at given point in the cycle. Inthe instances in which constant current is to be maintained in theflow-through capacitor, this means that voltage varies as the electrodestend toward saturation and a greater voltage potential must beestablished to maintain constant current.

Among the advantages realized by current-regulated operation (as opposedto voltage-regulated operation) is that by integrating the currenttransferred over the length of a single operational cycle it is possibleto determine an aggregate amount of ions or charged constituents thathave been collected on or discharged from the electrodes and/or theircorresponding membranes. This amp-second value or “ampsum”, which is theintegrated amperage value over time, can be compared to a known orcalculated total useful capacity of the flow-through capacitor todetermine when the electrode pairs of the flow-through capacitor havebeen saturated (i.e., approached their useful treatment limit) orde-saturated (e.g., approached a point at which most or all ions orcharged constituents have been discharged).

Accordingly, current-regulated operation provides a yet-unrealizedmethodology to control operation of a capacitive deionization system anda metric by which to enable superior efficiency of the capacitivedeionization system. By using current-regulated operation, the systemcan be configured to not continue to apply a voltage potential whenminimal or no transfer of ions or charged particles is occurring. Thisprevents, for example, the continued application of a voltage differencein treatment mode when a saturation point of the flow-through capacitorhas been reached.

Instead of directly monitoring and integrating current to establish theduration of a cycle and the capacity of the flow-through capacitor, awater property, value, characteristic, or parameter can be used (or aconcentration thereof). For example, by measuring the conductivity ofthe water stream or the conductivity removed (by comparison of the waterbefore and after processing by the flow-through capacitor) andintegrating this value over the time duration of a cycle, the amount ofcapacity utilized in the flow-through capacitor can be indirectlymeasured. Accordingly, in some embodiments of the method of theinvention, the “current” measurement and calculation can potentially bereplaced by other measured water qualities or properties, such as forexample, conductivity or hardness. To the extent that suchcharacteristics, values, or parameters correlate with current (i.e.,conductivity of water depends in part on the number of ions in thewater), they can serve as good proxies for operation.

FIG. 5 illustrates a method 500 of current-regulated operation accordingto one embodiment of the invention. It will, however, be appreciated,that rather than measuring and adjusting current another parameter canbe controlled such as, for example, a water property (e.g.,conductivity). According to the method 500, a summed-current capacity ofthe flow-through capacitor is established in step 502. Thesummed-current capacity corresponds to a useful capacity of the system.To draw an analogy, this summed-current capacity corresponds to theamount of ions or charged constituents the electrodes can support in thesame way that one could determine the amount of water that a spongecould absorb (either empirically or by calculation).

This summed-current capacity can be, for example, theoreticallycalculated based on qualities and traits of the capacitive deionizationsystem (e.g., using physical and chemical values and/or designparameters such as the number of modules, stack size, number ofelectrodes pairs, cell area and surface properties).

Alternatively, the summed-current capacity can be established byobservation or measurement. For example, the system can be run intreatment mode until the flow-through capacitor has reached a point ofsaturation or the water reaches a property limit (which can bedetermined by comparing the difference between the input and outputwater conductivities, as conductivity correlates with the number of ionsin the water). The flow-through capacitor can then be set to regenerateuntil all ions and charge constituents are driven from theelectrodes/membranes. During either treatment or regeneration, thecurrent can be integrated over time until no or little additionalcurrent is transferred. This measured value would correspond to theusable summed-current capacity.

In some embodiments, the system can use both methods and/or continue toperiodically re-calculate or re-establish the summed-current capacity.For example, the system can initially operate using a theoretical valueand then begin to monitor treatment or discharge cycles to furtherrefine the summed-current capacity value. In other embodiments, thesystem can continually or periodically monitor discharge or regenerationcycles to re-establish or revise the summed-current capacity for eachsubsequent treatment cycle. In still other embodiments, the system cancontinually or periodically monitor treatment cycles to re-establish orrevise the summed-current capacity. The flow-through capacitor can beoperated through multiple operational cycles until an equilibriumcapacity is reached or approached.

The system and controller can be permitted to operate at an imbalancebetween discharge and treatment cycles so that more energy is stored ineach treatment cycle than is discharged in the subsequent dischargecycle until enough of the capacity is used to achieve an optimumregeneration cycle. Thereafter, the system can operate in balance withthe energy discharged and the energy stored in each cycle to beapproximately equal.

In capacitive deionization systems, the summed-current capacity cantypically be between approximately 1000 amp·seconds and 2200 amp·secondsper stack and the area of the electrode pairs for each stack can beapproximately 5800 square centimeters. However, systems having higher orlower capacities can be also used. It will readily be appreciated thatdesign parameters can affect the summed-current capacity of a particularsystem.

Once a summed-current capacity is established according to step 502,then an operational cycle of the flow-through capacitor can be startedaccording to step 504. This operational cycle can be, for example, thetreatment mode, the regeneration mode, or the cleaning mode.

This operational cycle need not immediately occur after establishing thesummed-current capacity. For example, after establishing thesummed-current capacity, the system can be in a standby mode until thereis a demand for treated water. Moreover, this operational cycle need notbe completely continuous. For example, a treatment mode can be startedbased on the demand for water and then stopped temporarily until morewater is needed.

Once the operational cycle has been started, the controller monitors thecurrent and integrates the current over the time of the operationalcycle to determine a monitored-current value according to step 506. Overthe course of the operational cycle, this monitored-current value iscompared to the summed-current capacity according to step 508 todetermine whether (1) to continue to operate in the particularoperational mode if an endpoint condition has not been reached, in whichcase the system continues to monitor current according to step 506 andthen re-compare the summed-current capacity and monitored-current valueaccording to step 508 until the endpoint condition has reached or (2) toend the operational cycle according to step 510 if the endpointcondition has been reached. The condition that results in thetermination of the operational cycle at the endpoint can be, in oneembodiment, when the summed-current capacity is equal to themonitored-current value. In some embodiments, this can mean integratingand counting up to the monitored-current value to the summed-currentcapacity. In other embodiments, this can mean subtracting the monitoredcurrent value from the summed-current capacity until the resultant valueis equal to zero.

Some ions or charged constituents may be strongly connected to theelectrodes and/or membranes during treatment. As a result, there canalso be logic that permits the cycle to be terminated if the endpointhas been substantially reached, although not achieved. For example,after a period of discharge, a relatively small percentage of chargedparticles may not separate from the electrodes and/or membranes due tothe strength of their attachment. The system and controller can beconfigured to terminate the cycle if the summed-current value is within,for example, 5% of the endpoint and remained substantially at thatsummed current for a predetermined length of time. Such logic canprevent the system from becoming locked in a particular operational modewhen transfer becomes inefficient (or perhaps even impossible) due tochanges in the capacity of the flow-through capacitor.

In some embodiments, the system can undergo a partial treatment cycleand then, after a specified duration of inactivity, enter a dischargecycle to discharge only the collected amount of charge. In theseembodiments, the monitored-current capacity during discharge can becompared to the final monitored-current capacity in the prior treatmentcycle. Such operation can be used to restore the flow-through capacitorto its full capacity during lengthy periods of non-use or standby.

During continuous demand for treated water which exceeds the totalavailable capacity for the flow-through capacitor, a switch between thetreatment mode and regeneration mode can be based on the comparison ofthe summed-current capacity and the monitored-current value. Forexample, when there is a demand for water, the system can operate in thetreatment mode until the monitored-current value is equal tosummed-current capacity. At this point, the system can determine that nofurther useful treatment can be performed without first discharging thecollected ions and constituents. Accordingly, the system can switch tothe regeneration mode in which ions will be discharged from theflow-through capacitor until the comparison of the summed-currentcapacity and the monitored-current value indicates that the regenerationcycle should be stopped because an endpoint of the cycle has beenreached (i.e., all ions or charged particles have been discharged).

Alternatively, instead of comparing a summed value to a capacity valueduring regeneration, a fixed time regeneration cycle can be used. When afixed time is used, certain assumptions are made about the rate at whichconstituents are discharged that, when valid, simplify the regenerationcycle. For example, if the system is set to 20 amps and the regenerationcycle is run for a fixed time duration of 90 seconds, then (givenefficient transfer of the constituents from the electrodes to the water)1800 amp-seconds of capacity can be assumed to be regained.

The controller can be programmed so that under certain conditions (e.g.,high measured input or output water conductivities corresponding to highlevels of constituents and the flow-through capacitor having sufficient,but not full, regeneration), the system can be allowed to return to thetreatment mode without fully completing the discharge/regenerationcycle. Again, because current-regulated control of the system providesan accurate metric of the available capacity of the flow-throughcapacitor, complex logic such as this can be employed in systemoperation which was previously unavailable or in which availablecapacity would be, at best, a guess.

FIG. 6 illustrates one embodiment of an operational cycle in which thecurrent and voltage over the time or duration of an operational cycle.The top chart 610 illustrates current over time and the bottom chart 612illustrates voltage potential or difference over time.

As shown in the top chart 610, a current-time line 614 depicts thecurrent measurement over the time of the cycle, which ends at a time 616indicated by the dashed line. The current or amperage is held constantover at least a first portion of the cycle until it begins to taper offnear the end of the cycle at a second portion. However, in someembodiments, the current can be held constant over the entire length ofthe cycle (for example in a system having 1800 amp·seconds capacity, atreatment cycle can be at 20 A for 90 seconds).

One reason that the current can be held constant is to provide arelatively constant flux of ions and charged particles over the durationof the cycle. In some embodiments, however, current can be adjusted foractual operating conditions such as, for example, variations in feedwater conditions such as conductivity and flow rate. For example, if aflow rate of water flowing through the flow-through capacitor increases,then it may be desirable to increase the current to increase the flux ofions and charged particles between the electrodes and/or membranes andthe water. Likewise, a significant change in the observed conductivityof the water (indicative of a different amount of ions or chargedconstituents) can dictate an increase or decrease in the current oramperage level to obtain or maintain the desired water property or waterproperty concentration in the treated water. The current or amperagelevel can also be set or adjusted based on a treated water property orwater property concentration, such as treated water conductivity.

Still referring to the top chart 610, the shaded area 618 corresponds tothe total amp·seconds or ampsum of the cycle (i.e., the integral ofcurrent over time). As discussed above, through the course of the cycle,the integral taken from a zero time at the start of the cycle to apresent time in the cycle is the monitored current value which is thencompared against the summed-current capacity to determine the end pointor time of the cycle. With line 616 being the end time, the integralunder the amperage curve from the zero time to the end time (depicted asshaded area 618) also corresponds to the summed-current capacity of theparticular system.

As shown in the bottom chart 612, a voltage-time line 620 is used todepict the voltage over the time of the cycle. If the current oramperage is held constant, then the voltage may need to be increasedover the duration of the cycle to maintain a constant rate of ion flux.This may be a result of, for example, a decrease in the effectiveness ofthe applied voltage as the electrodes and/or membranes saturate withions or charged constituents. At some point over the cycle, it ispossible that a maximum voltage differential is reached based on thepower limitations of the system. When this happens, voltage may peak ata constant level and the flux of ions or charge may begin to decrease asthe constant voltage is of decreasing effectiveness as time furtherprogresses.

Formulas can be employed to convert the electrical capacity of thecapacitive deionization system to an ion capacity based on mEq(milliequivalents) and visa versa. Such formulas can be used to convertampsum information to useful information that can be passed to the enduser by the controller.

Standby Mode

When the system is not transferring ions, it can be placed in a standbymode. In the standby mode, the capacitive deionization system 10, 110,is in such a state that water is neither flowing into nor out of thesystem 10, 110 (or at least in such an appreciable quantity as torequire processing of the water). Since no water is actively flowingthrough the flow-through capacitor 26, 126, it is not necessary toeither draw constituents out of the water as happens during treatment orflush constituents from the capacitor into the water as happens duringregeneration or cleaning. Even in this steady state condition, someamount of voltage difference can be applied across the electrode pairs32 so that constituents do not migrate out of the cation membranes 35and the anion membranes 36 and into the water standing in theflow-through capacitor 26, 126.

In addition to preventing scaling when the system is in standby, anapplied voltage potential helps to prevent poor water quality on startup. This is because ions are less likely to migrate into the standingwater in the flow-through capacitor. After a particularly long period ofstandby, the system can be configured to send a predetermine volume ofwater to the drain in order to ensure that the initial volume water sentto the treatment outlet has not become impurity or constituent richwhile sitting stagnant in the flow-through capacitor or another portionof the upstream plumbing.

Treatment Mode

When there is a demand for treated water and water is flowing throughthe flow-through capacitor 26, 126, the system 10, 110 can enter thetreatment mode or purification mode. In the treatment mode, at least aportion the water or solution passes through the flow-through capacitor26, 126 with a voltage potential applied in the normal direction so thations and compounds or particles that exhibit charge attraction areattracted to the electrode pairs 32. These constituents are drawn out ofthe stream of the water and pass through the cation membranes 35 and theanion membranes 36 and are captured on the carbon electrodes 33, 34. Thestream of water, now having a portion of the constituents removed, canexit the flow-through capacitor 26, 126 in a comparably pure state tothe water that enters the flow-through capacitor 26, 126 and the treatedwater can be routed to the treated water outlet 76, 176.

Many variables can effect the rate and quantity of the ions and chargedconstituents removed from the water during treatment, including, but notlimited to, the voltage potential established over the electrode pairs32 (and the related amperage which is, in fact, the regulated portion ofthe capacitor), the flow rate at which water flows through theflow-through capacitor 26, 126, the flow pattern through theflow-through capacitor 26, 126, the inlet water quality, and to whatextent the constituents have saturated the membranes and/or electrodes.The flow rate can be adjusted using one or more valves, can be variablewithin minimum and maximum limits determined by the module configurationand/or operating conditions, and can be based at least in part on ademand for treated water. The amperage of the flow-through capacitor isdetermined by the controller 78, 178.

As a general rule, as the flow rate decreases and/or the amperageincreases, more ions or charged constituents per unit volume will betransferred between the water passing through the flow-through capacitorand the electrodes. Conversely, as the flow rate increases and/or theamperage decreases, fewer ions or charged constituents will betransferred per unit volume of the water.

One method of treatment 700 is illustrated in FIG. 7. According to themethod 700, a targeted water property (or water property concentration)or conductivity or a fixed percentage removal of a water property (orwater property concentration) or conductivity can first be establishedfor the treated water according to step 702. Then, some property of thewater, such as the conductivity of the feed water (although otherqualities can also be used), is measured according to step 704. Sincethe capacitive deionization system removes ions and charged particles tomake the water more pure to a desired water property, the controller isthen able to determine the amount of conductivity that must be removedfrom the feed water in the flow-through capacitor to achieve the targetwater property (i.e., the treated water conductivity) or a percentageremoval in step 706. Based on this conductivity to be removed, thecontroller can control one or both of the current or amperage of theflow-through capacitor and the flow rate of water through theflow-through capacitor to achieve the desired resultant property in thetreated water stream according to step 708. The conductivity of thetreated water can be measured to confirm the effective removal of ionsand charged constituents. There can be limits on the treatment levelachieved. For example, water that is too pure could cause issues withresidential plumbing, and cause too much resistance in the cell, whichwould result in high voltages required for treatment and less efficienttreatment.

Once a particular water property or percent removal is targeted orselected, a volume can be calculated that corresponds to the amount ofwater that can be fully treated in a treatment cycle given that property(e.g., conductivity) in the feed water. Such a volume can be establishedby considering the summed-current or total usable capacity of theflow-through capacitor (which represents the amount of charge that canbe received from the water) and amount of conductivity to be removedfrom the water (which corresponds to the amount of ions or chargedconstituents to be removed per unit volume of water to achieve a desiredwater property). In some installations or points of entry, it can beacceptable to assume that the feed water conductivity will remainrelatively constant and so the controller can use this calculated volumeas a basis for determining the length of the treatment cycle. Under suchconditions, the amperage can be adjusted or varied based on the flowrate to continually remove a particular charge per unit volume oftreated water so that the treatment cycle is set to end when thecalculated volume of water has been treated.

According to some embodiments of the method, the flow rate through thesystem can be determined by and, in some instances, change with thedemand for treated water. The demand for water can be provided bymonitoring the pressure in the hydropneumatic water tank and/or the tankwater level in an atmospheric tank. If the pressure or water level dropsbelow a certain threshold level, there is generally increased demand fortreated water. It is possible that demand can be observed as a binarycondition (i.e., either more water needs to be treated or it does not)or that there can be various levels of water demand, either stepwise orcontinuous, based on an observed pressure or level sensor value. Forexample, the degree or amount of pressure drop in a hydropneumatic tankcan be used to establish the magnitude of the demand for water.Additionally, a flow sensor or sensors can be used to determine thedemand for water.

In low demand situations, the system can generally meet the demand fortreated water. In such instances, the flow-through capacitor can beinstructed to only treat the water to a targeted water property orpercentage removal to save energy and capacity of the flow-throughcapacitor or can be instructed to treat the water to be as pure aspossible. Moreover, in some instances, treated water can bere-circulated one or more times to further remove constituents from thewater.

In high demand situations, the flow rate of the water to be treated canexceed the ability of the flow-through capacitor to process the water tothe desired property. When this happens, the system can treat the waterto the extent possible and allow the treated water to be of less thanthe desired quality or purity. This may be preferable to not providingwater in a sufficient quantity to meet point of use demand. The removalrate can be lowered by allowing the system to operate at a treatmentcurrent or amperage less than the current calculated to provide thedesign removal percentage. Likewise, to prevent the cell of theflow-through capacitor from exceeding its maximum operating voltage, thetargeted change in feed water conductivity or other measured propertycan be limited. The controller can be set to end the treatment cycle ifa preset or calculated treated volume is exceeded, a time length ofcycle has been exceeded, and/or maximum voltage has been reached.

It is also contemplated that varying the flow rate in a cycle can helploosen or remove scaling and/or fouling during treatment. Particularly,in instances in which the water is being stored prior to use, it can bebeneficial to cycle the flow rates between higher and lower values toalter flow patterns and the applied shear force of water on the surfacesof the flow-through capacitor.

Additionally, various aspects of the treatment cycle can be used orconsidered to adjust the summed current capacity of the system. Forexample, over the course of the treatment cycle, the time to reach themaximum voltage can be determined. A decrease in this time over variouscycles can indicate a loss of capacity in the flow-through capacitor. Asstill another example, the percentage of the summed-current capacityrealized before the maximum voltage is reached can be used to determinea loss of capacity of the system. As the percentage of system capacityused before maximum voltage is reached decreases, so does the usablecapacity of the flow-through capacitor. Based on either of theseobserved conditions, the summed-current capacity of the system can beadjusted and/or the regeneration cycle can be triggered.

In another embodiment of the treatment mode, the treated waterconductivity (as opposed to the feed water conductivity) can be measuredto determine whether to adjust the amperage of the flow-throughcapacitor. Given that feed water quality may be relatively constant, itmay be acceptable to adjust the amperage up or down based solely on themeasured treated water conductivity. Such an adjustment can be suitableto accurately adjust the conductivity to be removed, even in situationswhere the feed water conductivity is unknown.

In still other embodiments, a water property other than waterconductivity can be used as the basis for determining the amperage atwhich to run the flow-through capacitor. For example, a pH or alkalinityof the water can be used as a monitored water property.

Moreover, in the event that the treated water purity is believed to beapproaching a minimum acceptable water property or is continuallyrunning below the target water property, the system can be set to alarmor store the event as a fault condition. This can alert the user to adeficiency in the system and a need for maintenance of the system or theinability of that particular size of system to continually meet thedemand for treated water at that point of use.

Regeneration Mode

Once the electrodes become saturated with ions during the treatmentmode, the electrodes 33, 34 can have their capacity regenerated during aregeneration cycle. During regeneration, the electrode pairs 32 areshorted or the voltage potential is reversed and the ions (and compoundsor particles that exhibit charge attraction) are driven off of thecapacitor's electrodes 33, 34 and/or the membranes 35, 36. This processforms an impurity or constituent-rich concentrated solution in the flowspacer 37 which is then hydraulically discharged from the flow-throughcapacitor 26, 126 typically through the drain 58, 158. The watercarrying the discharged constituents will be directed to a waste wateroutput or drain 58, 158 until substantially all the constituents arereleased or the target capacity is restored (although some constituentsmay be so strongly attached to the electrodes and/or membranes as to notbe readily detachable). Once some or all of the capacity of theflow-through capacitor 26, 126 is recovered, then the flow-throughcapacitor 26, 126 is again ready for ion or impurity removal in thetreatment mode.

The ions released by the electrodes can include hardness ions, such ascalcium, and alkalinity ions, such as carbonate and bicarbonate ions. Ifthe concentration of these ions in the waste water becomes too high,these ions can precipitate and form scaling on the spacer 37. Scaling ina flow-through capacitor can clog up the water flow path and possiblyalso contaminate the electrodes, particularly the cathode. This maynegatively influence the performance of the flow-through capacitor oreven cause the flow-through capacitor to stop working. While periodicregeneration and cleaning helps to improve the usable life of thesystem, it ideally should be performed in such a way as to not impairthe long-term performance of the system by forming scaling.

In some embodiments, to improve the efficiency of the regenerationcycle, the regeneration mode can be performed with clean water, purifiedwater and/or chemicals to clean the system. However, in the most basicembodiment, feed water can serve as the transport agent for thedischarged ions.

During some forms of regeneration, the system or controller can comparea monitored-current value (i.e., the ampsum of the discharged ions)during the regeneration cycle to the final monitored-current value ofthe previous treatment cycle or the summed-current capacity of theflow-through capacitor to determine the endpoint of the regenerationcycle as described above. The monitored-current value for theregeneration cycle is an integral of the current over time which willcorrespond to the amount of charge constituents transferred from theflow-through capacitor to the water stream over the time of theregeneration cycle.

In some embodiments, the regeneration mode can be initiated and allsteps within the regeneration mode can be started or terminated based ontime and/or a change in the water property as measured by (withoutlimitation) conductivity, pH, ORP (oxidation-reduction potential),specific ion electrode or other means. Moreover, one or more of feedwater hardness, pH, alkalinity and conductivity can be measured and usedas a basis to calculate a maximum discharge conductivity under which thepotential for scaling is reduced.

While the net ion flux during the regeneration cycle will be from theelectrodes and/or membranes into a discharged stream of water, thecurrent or amperage and the flow rate can vary over the length of thecycle. For instance, the regeneration cycle can have portions where theelectrodes are shorted, where the electrodes are set to a reversepolarity, and even where the electrodes are temporarily set to a normalpolarity. Additionally, the flow rates can be adjusted in magnitude (lowrates and high rates) and direction (forward, reverse, and no flow). Insome embodiments, to reduce water usage, but to maintain a flow, watercan be, at least to some extent, re-circulated through the flow-throughcapacitor during regeneration.

The concentration of ions or charged constituents in the dischargedwater can be controlled to reduce the potential for scaling and/or toprovide time efficient discharge of the collected ions and chargedconstituents according to the method 800 illustrated in FIG. 8. As withtreatment, the flow rate and amperage can be controlled to adjust therate at which ions and charged constituents are transferred into thewater and the volume of water exposed to this ion flux.

According to the method 800, a targeted water property (e.g., a maximumimpurity level of the discharge stream) or percent addition ofconstituents can be established according to a step 802. This propertyin the feed water (e.g., a conductivity of the water) can then bemeasured according to step 804 before it is received in the flow-throughcapacitor. According to step 806, the targeted water property and themeasured feed water property can be compared to determine what amount ofthe property, such as conductivity in the form of ions, can be added perunit volume of the feed water to provide a discharge stream having thetargeted water property or added percentage of the water property ofinterest. Based on this calculated value, the flow rate through theflow-through capacitor and/or amperage of the flow-through capacitor canbe altered according to step 808 to add the impurity to the dischargestream from the electrodes and/or membranes in the flow-throughcapacitor.

Accordingly, in one embodiment of the method, by controlling thedischarge amperage or amperage set point, measuring the feed waterconductivity or other water property parameter, calculating the iontransfer rate from the discharge amperage, calculating the flow raterequired to control concentration of the discharged water and using avalve or other method to control the water flow to achieve that flowrate, the concentration and/or amount of the impurity transferred to thedischarged water can be controlled. Similarly, the concentration and/oramount can be changed by adjusting the current or the current set pointbased on the discharge water rate and the measured feed waterconductivity or other water property parameter based on the calculatedion transfer rate. Formulas can be used to calculate flow rates fordilution in regeneration based on feed water conductivity and iondischarge rate.

According to one embodiment of regeneration, multiple flow rates can beused to save water while simultaneously preventing the concentration ofions and/or constituents in the water from exceeding a maximum allowableconcentration. The flux of ions and constituents into the water willinitially be high and then decrease over the length of the regenerationcycle. This means that the water flowing through the flow-throughcapacitor can initially be provided at a high flow rate to receive andtransport the initial high levels of ion flux. As ion flux decreases,the flow rate can be reduced because fewer ions need to be transportedout of the flow-through capacitor per unit time. Accordingly, at the endof the regeneration cycle, the water can dwell within the flow-throughcapacitor for a longer time than at the beginning of the cycle withoutapproaching the maximum acceptable impurity level for discharged water.

In some embodiments of the regeneration mode, the flow rate of the watercan be pulsed to reduce the amount of water used or to provide variableflow rates to inhibit scaling. As described above with respect to thetreatment mode, toggling high and low flow rates can be used to loosenor remove scaling and/or prevent fouling during regeneration.

In still other embodiments of the regeneration mode, flow can betemporarily reversed during ion and charged impurity discharge. If theflow is reversed, it is possible that the drain can be disposed upstreamof the flow-through capacitor, so that the impurity or constituent-richwater flowing in reverse can be removed from the system prior to theflow-through capacitor.

The controller can limit various aspects of the operation of theflow-through capacitor during the regeneration mode. For example, theregeneration flow rate can be variable with minimum and maximum limitsdetermined by module configuration and controlled by the valveconfiguration. Additionally, the regeneration mode can be set toterminate based on a number of factors including excessive length oftime, excessive amperage, or comparison of the monitored-current valueto a final treatment monitored-current value or a summed-currentcapacity of the system. Likewise, these conditions can be used assuggested above to alter the summed-current capacity of the flow-throughcapacitor.

Additionally, the controller can be configured to ensure that the flowrate does not go below a minimum regeneration flow rate set to ensurewater distribution throughout the cells. If the flow rate were to becometoo low during regeneration, localized areas of highly concentrateddischarge water could be created which could result in undesirablescaling on, for example, the flow spacer.

Cleaning Mode

As briefly mentioned above, once attached to the electrodes and/ormembranes, some ions may not be easily removed. These ions may requiresomething more than a standard discharge cycle to be removed. Although ahigher loading of ions has been found to actually improve the kineticsof ion transfer during transfer, too many strongly attached ions canhave an adverse effect on the capacity of the system.

Accordingly, the system can occasionally enter a cleaning mode in whichthe system undergoes more time intensive regeneration processes. Thesecan include longer regeneration modes with greater voltage differencesor pulsing voltages, variable flow rates, the use of a cleaner or otherprocess variations to remove hard to detach ions from theelectrodes/membranes.

The system and controller can be set to automatically enter a cleaningmode when one or more of a number of conditions are met including, butnot limited to, a threshold number of cycles have been performed, athreshold treated volume of water has been processed, the system hasremained in standby for a duration of time, a significantly highpressure drop is observed over the flow-through capacitor, a time orwindow of time of the day is occurring, and a loss of capacity isobserved.

If the system is unable to restore the system capacity to a particularlevel during cleaning, the system can be set to provide a loss ofcapacity alarm. Such an alarm can help the end user to determine whencomponents need to be replaced or otherwise maintained.

It will be appreciated by those skilled in the art that while theinvention has been described above in connection with particularembodiments and examples, the invention is not necessarily so limited,and that numerous other embodiments, examples, uses, modifications anddepartures from the embodiments, examples and uses are intended to beencompassed by the claims attached hereto. The entire disclosure of eachpatent and publication cited herein is incorporated by reference, as ifeach such patent or publication were individually incorporated byreference herein.

Various features and advantages of the invention are set forth in thefollowing claims.

What is claimed is:
 1. A method of regenerating a capacity of aflow-through capacitor having at least a pair of electrodes spaced fromone another to accommodate a flow of water and configured to transferions between the pair of electrodes and the water, the methodcomprising: establishing a target value for a water propertyconcentration in a discharge water stream exiting the flow-throughcapacitor; measuring a feed value for the water property concentrationin a feed water stream entering the flow-through capacitor; calculatingan amount of the water property concentration to be added to the feedwater stream based on the feed value to achieve the target value for thewater property concentration in the discharge water stream; andcontrolling an amperage of the flow-through capacitor and a flow ratethrough the flow-through capacitor to add ions to the feed water streamto achieve the target value for the water property concentration in thedischarge water stream.
 2. The method of claim 1 wherein the amperage isa function of an amount of ions to be added to the feed water stream. 3.The method of claim 2 wherein the amount of ions correlates to theamount of the water property concentration to be added to the feed waterstream.
 4. The method of claim 2 wherein the amperage is further afunction of the flow rate.
 5. The method of claim 1 wherein the waterproperty concentration correlates to conductivity and the feed valuethat is measured is conductivity.
 6. The method of claim 1 furthercomprising limiting the amount of the water property concentration to beadded at a given flow rate based on a voltage limit of the flow-throughcapacitor.
 7. The method of claim 1 further comprising the step ofmeasuring the water property concentration of the discharge water streamexiting the flow-through capacitor and altering control of at least oneof the amperage and the flow rate if a measured value of the waterproperty concentration is different than the target value.
 8. The methodof claim 1 wherein the flow rate is pulsed during a discharge cycle tosave water.
 9. The method of claim 1 wherein a direction of flow throughthe flow-through capacitor is reversed during a discharge cycle incomparison to a forward direction during a treatment cycle.
 10. Themethod of claim 1 wherein an end point of a discharge cycle isestablished when a maximum voltage of the flow-through capacitor isreached.
 11. The method of claim 1 wherein the flow rate is varied overa time duration of the discharge cycle to inhibit scaling.
 12. Themethod of claim 1 wherein an end point of a discharge cycle isestablished by a comparison of a monitored-current capacity of theflow-through capacitor over the duration of the discharge cycle to asummed-current capacity of the flow-through capacitor that ispre-established.
 13. The method of claim 12 wherein an end point of adischarge cycle is established when a maximum voltage of theflow-through capacitor is reached and the summed-current capacity of thesystem is adjusted based to be a monitored-current capacity at themaximum voltage.
 14. The method of claim 1 wherein an end point of thedischarge cycle is established when at least one of a pre-determinedvolume of the discharge water stream has been purged at a fixed amperageand a duration of the cycle is reached.
 15. The method of claim 1wherein the flow rate has maximum and minimum flow rates.
 16. The methodof claim 15 wherein a minimum flow rate is set to ensure waterdistribution throughout the flow-through capacitor thereby inhibitinglocalized areas of highly concentrated discharge water and scaling. 17.A controller configured to perform the method of claim
 1. 18. A methodof regenerating a capacity of a flow-through capacitor having at least apair of electrodes spaced from one another to accommodate a flow ofwater and configured to transfer ions between the pair of electrodes andthe water, the method comprising: establishing an amperage set point forthe flow-through capacitor and a target concentration for a waterproperty concentration in a discharge water stream exiting theflow-through capacitor; measuring a feed value for the water propertyconcentration in a feed water stream entering the flow-throughcapacitor; calculating an ion transfer to the feed water stream based onthe amperage set point and a flow rate required to achieve the targetconcentration for the water property concentration in the dischargewater stream; and controlling the flow rate through the flow-throughcapacitor to achieve the target concentration for the water propertyconcentration in the discharge water stream while maintaining theamperage set point of the flow-through capacitor.
 19. The method ofclaim 18 further comprising: adjusting the amperage set point; andrecalculating and adjusting the flow rate to achieve the targetconcentration for the water property concentration in the dischargewater stream based on the adjustment to the amperage set point.
 20. Acontroller configured to perform the method of claim 18.